When designing industrial robots, it is common to arrange the cable harness, necessary for the robot, internally of the robot. For welding robots, it is equally common for the cable harness to be arranged so as to extend outside the upper arm of the robot up to an offset welding gun. This provides a space-demanding arrangement. In the case of internally extending cable harnesses, there is always a risk of hooking onto, for example, a workpiece, such as a car body. The risk of hooking is especially great if the cable harness is running freely outside the upper arm of the robot up to the tool.
In both externally and internally extending cable harnesses, problems with deformation and torsion of cables and wires arise. Problems arise in particular when the robot is to be able to bend its wrist more than 90°. Cables, for example for electric power to welding electrodes, power supply to tools and robot, electric signal cables for transmission of information from sensors at the welding head, hoses for compressed air and coolant etc. are to manage the necessary bending while simultaneously rotating in spite of the fact that they provide considerable resistance to such bending and rotation.
When positioning the working tools of an industrial robot, problems arise when the cable harness extends externally. The rapid movements of the robot result in an externally extending cable harness flinging round the upper arm of the robot and result in a deterioration of the working accuracy of the robot. The solution so far has been to control the speed and hence reduce the speed of the robot before, for example, welding operations in order to reduce the unwanted movements of the cable harness and hence to attempt to maintain an acceptable welding accuracy.
The term cable harness here refers to a process cable harness, which may be surrounded by a casing for, for example, welding electrodes, power supply for the tool itself and/or power supply to the robot. In addition, the term comprises spare wires for, for example, the various requirements of the client.
The prior art comprises industrial robots for, for example, welding applications, which are arranged with the process cable harness extending with a considerable offset with respect to the three axes of rotation in the upper arm. These solutions are space-demanding.
One long-felt need is that of a space-saving robot. The need primarily applies to a space-saving upper arm and wrist, which may enter into narrow spaces. To this is to be added the robot user's need of a flexible robot design that facilitates replacement of robot application. When manufacturing car bodies, for example, there is a need of a compact robot arm for welding applications, that is, a robot arm provided with a welding cable harness.
This need cannot be fulfilled by any of the industrial robots disclosed in the cited documents.